Preparation of hydrogels by radiation copolymerization of acrylamide and sodium acrylate was investigated. Monomer concentration of mentioned system may be increased from 20 wt.% to 50 wt.% by adding small amount of non-ionic surfactant. The polymerization conversion and intrinsic viscosity of copolymers in high monomer concentration are greater than that in low monomer concentration to a certain extent. Radiation crosslinking of copolymer gives hydrogels having swelling ratio in water above 1,000, The swelling ratio of the copolymer-hydrogels depends not only on the crosslinking density, but also on the amount of -COONa groups in macromoleculer chains.